1. Field of the Invention
The present invention relates to punch dies and, more particularly, to a punch die for a punch machine.
2. Discussion of the Related Art
Referring to FIG. 3, a related-art punch die 10 includes an upper die 12 and a lower die 14. The punch die 10 is generally installed on a punch machine 20, and configured to punch a metallic workpiece. The punch machine 20 includes a base set 22, and a bracket 24 supported by the base set 22. The upper die 12 is attached to the bracket 24, and can be moved downwards by a first cylinder 242. The lower die 14 is disposed on the base set 22. A blank holder 16 is sleeved on the base set 22. A second cylinder 222 is disposed in the base set 22. The second cylinder 222 is connected to the blank holder 16 for providing a constant force to the blank holder 16.
The second cylinder 222 is disposed in the base set 22. When the second cylinder 222 breaks down, the punch machine 20 should be hoisted up so that the second cylinder 222 can be taken out of the base set 22 for repairing. As such, it is very cumbersome to repair the second cylinder 222. Thus, the blank holder 16 is generally replaced by a spring or an air cushion that is easily disassembled. When a metallic workpiece is punched, the spring or the air cushion applies a force to the metallic workpiece. The force is related to a force provided by the second cylinder 222 and the compression of the spring or the air cushion. Since the compression of the spring or the air cushion is often inconstant, the force applying to the metallic workpiece is unstable, which leads the punched workpiece to have an unstable size.
Therefore, a punch die and a punch machine using the same which is easily repaired and can punch a workpiece with a stable size.